deformation in welded rectangular steel tank 1

[javed13]

? The long walls of a 40' x 10' x 10' rectangular stainless steel tank consist of four - 20' x 5' plates welded together. The lower plates on the long wall of the tank has deformed by bulging out and deforming inwards. The lower plates on the opposite long wall has deformed in opposite manner by deforming inwards and bulging out respectively. It appears that the tank has twisted. The tank is suppoted on pile caps and the foundation is level. Looking for a method to straightening the bulge and inward deformation and reinforcing the tank with stiffners.

 

[JedClampett]

Steel plates are a really inefficient material for building rectangular tanks. Fixing it is pretty straightforward. You drain the tank. If the deformations are inelastic, you're going to have to remove the permanent portion of the bending. Probably going to be a lot of labor and not look too great afterwards. You then analyze the tank using a finite element program or traditional beam theory. You're likely to find some pretty big stresses for the original design. Note that if you use a finite element program it will require reinforcing the tank in two direction, while if you do it by hand, you can pick a direction of analysis and reinforcing (horizontal or vertical). Tying the top of the tank together will help a lot with your stresses. Of course it makes getting in the tank much more difficult.
Stainless angles are the traditional method for reinforcing stainless steel plates, although tees or plates (perpendicular to the walls) work. You can use the same size angle and adjust the spacing to match your stresses. Make sure the attachment points (corners and bottom) are checked.
There's a price point where it's cheaper to replace the whole thing with a concrete tank. But I suspect that whoever made the (boneheaded) decision to go with stainless is not going to like completely changing the design.
I've done several designs on rectangular metal tanks. When the powers that be realize how messy and ugly they look when properly done, they usually listen and go with concrete. But not always.

 

[javed13]

Thanks Jed for a such a clear explanation based on experience and theory. I didn't think I could get any response to my question. But, thanks again. It shows that large rectangular steel tanks are fabricated eventhough they could deform substantially with time. I was wondering why on earth anybody would consider 10' tall welded tanks with a couple of horizontal stiffeners and tie rods connecting the long walls. Instead of tie rods a better option might have been to have sufficient vertical stiffeners along with the two horizontal stiffeners. as usual complete design or as-built drawings were unavailable and one would have to empty the tank to know as-built sections.